1. Field of the Invention
This invention relates to the field of chemistry. More particularly, this invention relates to saturable absorber materials. Still more particularly but without limitation thereto, this invention relates to a Q-switch for use at 1.00 to 1.80 micrometers, to be used in combination with a laser to give an effective high peak power output.
2. Description of the Prior Art
A Q-switch is used to increase the pulse power of a laser by shortening the output pulse duration. This process allows energy storage within the lasing medium prior to activation of the switch. Saturable absorbers are commonly used to change the Q (quality factor) within a laser cavity. Such materials normally operate using singlet state electronic transitions. A saturable absorber usually affects the modes of the lasing medium.
A saturable absorber is considered to be a passive Q-switch since no external control other than the laser beam itself is used to activate it. A passive device is preferred because of its simplicity since no complicated high voltage electronic timing circuits are involved.
A major disadvantage with the use of most saturable absorbers is their photo-instability. This photo-instability increases for organic dye saturable absorbers (the most common type) whose lowest energy singlet state electronic transition is in the near-infrared. Thermal energy is sufficient to cause a continued small percentage of electronic transitions. Energy-rich electronically excited molecules are usually more chemically reactive than ground state molecules. In addition, the low energy electronic transitions are usually the result of long chain .pi.-type resonance groups. Such large molecules tend to be insoluble and are difficult to synthesize.
Research has been done in the area of dyes which exhibit a long-lived second triplet state, see J. Faure, L. Grajcar, J. Baudet and G. Berthier, "Triplet-Triplet Absorption Spectra in Cyanine Dyes. Evidence for a Long-Lived Second Triplet State", IX IUPAC Symposium on Photochemistry, pp 108-109 (July 25-30, 1982). Since triplet state molecules can be chemically reactive, the choice of the absorber material and the conditions with which it is used would be critical to the expected useful life of the saturable absorber. Such parameters would best be optimized with respect to the intended usage of the saturable absorber.